Privacy is a concept that has been debated and argued throughout the last few millennia by all manner of people. Its most striking feature is that nobody seems able to agree upon a precise definition of what it actually is. In order to discuss privacy in any meaningful way a tightly defined context needs to be elucidated. The specific context of privacy used within this document is that of "personal data", any information relating to a data subject; a data subject is an identified natural person or a natural person who can be identified, directly or indirectly. This context is highly relevant since a lot of work within the IETF involves defining protocols that can potentially transport (either explicitly or implicitly) personal data. This document aims to establish a basic lexicon around privacy so that IETF contributors who wish to discuss privacy considerations within their work can do so using terminology consistent across the area. Note: This document is discussed at https://www.ietf.org/mailman/listinfo/ietf-privacy